It is common practice in the art of internal combustion engines to provide an air/fuel mixture carburetor having a throttle plate situated in a throttle body in the path of flow of a combustible air/fuel mixture. The throttle valve element is located on the downstream side of a venturi which develops a venturi pressure at its throat to facilitate distribution of fuel to the intake air. In the case of a liquid fuel carburetor, atomization occurs at the point of entry of the fuel into the carburetor throat. In the case of a carburetor assembly for a natural gas engine, atomization, of course, is not required; but the negative pressure developed at the throat of the venturi is used to obtain a flow of natural gas in the region of the venturi throat where it may mix with intake air. The resulting air/fuel mixture flow is controlled by the throttle plate at a point downstream from the venturi section.
It is usual practice in carburetor assemblies of this type to control the position of the throttle plate by means of a throttle plate actuator gear train or a complex throttle linkage mechanism which would be under the control of an operator-controlled throttle element.
Attempts have been made in prior art designs to simplify the throttle linkage mechanism by using a direct-drive connection between the throttle valve lever and the throttle plate so that an intervening gear train or throttle linkage is not required. This substantially reduces cost, reduces complexity of design, and improves reliability.
An example of a direct-acting throttle valve plate and plate actuator assembly is shown in prior art U.S. Pat. No. 4,779,592 wherein a stepper motor under the control of an electronic processor for an internal combustion engine is connected directly to a throttle shaft to which is secured a throttle plate located in an air intake passage for an internal combustion engine. The throttle plate is carried by a throttle shaft that is journalled and supported on the wall of the air intake passage. The throttle plate is fixed to the shaft so that no adjustment of the throttle blade with respect to the shaft may occur. The shaft is connected also to an accelerator pedal by a throttle linkage mechanism so that, as the accelerator pedal is depressed, appropriate throttle blade adjustments are made.
An electronic control system in the system disclosed in the '592 patent is adapted to detect vehicle wheel slip if the vehicle is running on a low friction surface. When slip is detected, an appropriate signal is developed by the microprocessor to adjust the stepper motor to compensate for the slip and to reduce the throttle setting, thus reducing engine torque in order to reduce the degree of wheel slip in a transient fashion. After the slip condition is avoided, the stepper motor will respond to a change in the magnitude of the slip signal by adjusting the throttle blade to the original position determined by the accelerator pedal position selected by the operator.
Other examples of a remote operator for a throttle blade are shown in U.S. Pat. Nos. 4,850,319 and 5,003,948 wherein a throttle blade for a carburetor for an internal combustion engine is actuated by an electronic throttle actuator directly connected to the throttle blade. The actuator of these prior art designs is in the form of a stepper motor which can adjust the throttle blade angle throughout a wide range of positions between a wide open-throttle position and a closed-throttle position. A throttle blade is located in the flow path for the air/fuel mixture and the blade is fixed to the shaft. The shaft itself is mounted in bearings located on opposite sides of the air flow passage.